Road milling bits and bit holders, the design of which, when made in differing sizes, can also be used for trenching machines and mining machines, have benefited greatly from what has been termed a “quick change tooling system,” found in the instant inventor's prior U.S. Pat. Nos. 6,371,567; 6,685,273; and 7,883,155.
In applicant's recently filed, provisional patent application, Ser. No. 61/944,676, filed Feb. 26, 2014, now application Ser. No. 14/628,482 filed Feb. 23, 2015, applicant discloses the findings that most of the retaining force between the diametrically compressed slotted portion of the shank in a quick change system and the base block bore is radially located near the top of the slotted portion of the shank. Indeed, the further one gets from the top of the slot, the less the distal end of the approximately 2½ inch long shank applies force to the base block bore.
In applicant's copending application, identified above, applicant has shortened the shank from a full length of approximately 2⅜ inches to about 1½ inches in length and has obtained about the same retention force between the bit/holder shank and the base block bore, between about 5,000 and 30,000 pounds of radial force.
A need has developed for providing additional access to the rear of a base block for removing a bit, a bit holder or a combination bit/holder.